1. Field of the Invention
This invention relates to the production of polyhydroxy acid (PHA) filamentary products, particularly bioabsorbable products. An aspect of this invention relates to a process for making PHA filamentary products at high speed and with.gtoreq.2X stretch orientation (a draw ratio.gtoreq.2:1). Still another aspect of this invention relates to a method for using lubricant for facilitating the stretch orientation of filaments.
2. Description of the Prior Art
Bioabsorbable filamentary products compatible with living tissue have been used for decades. For example, surgical wounds can be closed with the aid of such products (sutures, clamps, etc.). Over a period of time, the product gradually loses its physical strength as it becomes absorbed into the wound site, and it also seems to disappear because of its compatibility with or susceptibility to degradation by living tissue. However, enough physical strength is retained by the product to hold the wound closed until a considerable amount of healing has taken place.
Early on, bioabsorbable monofilament surgical products were developed from naturally-derived collagen materials (e.g. the so-called "catgut" sutures), and these collagen products are still in use today, but it has long been recognized that collagen products and particularly monofilament collagen products have certain inadequacies, such as nonuniformity and antigenic characteristics. "Poly(hydroxy acid)", i.e. poly(hydroxycarboxylic acid) or "PHA," monofilament and polyfilament (e.g. braided) surgical products have become welcome additions in the field of surgical products, due to their uniformity and predictability. (The PHA polymers are polyesters containing repeating hydroxycarboxylic acid units.) However, some of the essential mechanical properties of bioabsorbable PHA surgical products can only be obtained when the freshly-spun filaments are drawn (stretch-oriented). See U.S. Pat. No. 3,297,033 (Schmitt et al), issued Jan. 10, 1967 and U.S. Pat. No. 3,636,956 (Schneider), issued Jan. 25, 1972. For an early appreciation of stretch orientation of PHA fibers, see U.S. Pat. No. 2,683,136 (Higgins), issued Jul. 6, 1954.
The chemistry of the polymers that contain repeating hydroxycarboxylic acid units and that are suitable for the production of filaments or fibers is described in detail in U.S. Pat. Nos. 3,636,956, 3,839,297, 4,033,938, 4,243,775, 4,300,565, and 4,700,704.
For suture use, monofilaments were initially used. However, particularly in the case of PHA surgical products, it is generally conventional to spin a fine filament and then improve its handling characteristics, tensile strength, knotting strength, etc. by twisting together or braiding or otherwise combining several fine filaments into a multifilament structure, as in, for example, U.S. Pat. Nos. 3,297,033; 3,839,297 (Wasserman et al), issued Oct. 1, 1974; and 4,027,676 (Mattei), issued Jun. 7, 1977.
Although these synthetic sutures have excellent use properties, their production is relatively slow. For example, excessive breakage of the small denier individual filaments during the conventional processing steps of spinning, drawing to orient, annealing, and one or more wind-up steps can slow down production. Because of this breakage problem, the freshly-spun filaments are generally collected at relatively low speeds and then drawn in a separate step in which the drawn fiber is also collected at relatively low speeds (e.g. &lt;100 m/min.), in some cases as slow as just a few meters per minute. See Example 8 of U.S. Pat. No. 4,300,565 (Rosensaft et al), issued Nov. 17, 1981, wherein the collection speed of the drawn filament is 5.2.times.10 feet/min or about 52 ft./min. Nevertheless, as indicated above, drawing or stretch orientation can be vital to the production of surgical products of good quality.
In the field of filament processing generally, processing finishes or lubricants have been used to minimize running tensions and filament-to-filament friction, reduce static buildup, prevent filament breaks due to running tension, etc. See U.S. Pat. No. 3,296,063 (Chandler), issued Jan. 3, 1967. Chandler's finishes do not appear to be hygroscopic, but other prior art finishes can pick up moisture (e.g. atmospheric moisture). The PHA filaments preferred for use in surgical structures are water-sensitive, and some are rather easily hydrolyzed, resulting in polymer degradation and loss of physical properties. Accordingly, finishes or lubricants for PHA filament processing must be carefully formulated to accommodate the peculiar problems of these polymers.
Various finishes have been used as coating materials on spun PHA filamentary products, typically prior or subsequent to processing these products into sutures, e.g. to improve handling properties, knot tying strength, etc. See U.S. Pat. No. 4,027,676, U.S. Pat. No. 3,954,635, and U.S. Pat. No. 3,297,033. U.S. Pat. No. 3,954,635 (Cummings et al) mentions the problem of flaws in the fiber which arise due to passage of the fiber through processing machinery (e.g. braiding apparatus). Typically, Cummings et al form the fiber into a yarn and then draw it at a ratio such as 4:1 and a temperature of 140.degree. F. (60.degree. C.) to obtain a yarn of, say, 50 denier.